The present invention relates generally to the field of metal working and in particular to an improved tube extracting device for facilitating the removal of tubes from different types of structures, such as boilers, condensers, evaporators, heat exchangers, and the like.
A typical heat exchanger comprises a pair of parallel tube sheets, a plurality of baffle plates, and a plurality of heat exchanger tubes. The tube sheets are located at the ends of the heat exchanger. The baffle plates are positioned between the tube sheets and generally parallel thereto. The tubes extend between the tube sheets and through the baffle plates and are supported by the tube sheets. The tube sheets and baffle plates have a series of aligned holes formed therein, and the tubes are inserted through these holes and then expanded in the areas of the tube sheets into fluid-tight pressure contact therewith.
Because of malfunctions or normal preventive maintenance, it may be necessary to remove one or all of the tubes from the structure. To replace the tubes they are generally cut between the tube ends and the expanded ends of the tubes forcibly withdrawn from the tube sheets an inch or two until they can be withdrawn by hand. Tubes are also conventionally removed by the use of an air hammer or the like, chipping away at the tube connection to the drum, to physically force the tube from the associated opening in the boiler drum. These methods have often resulted in damage to the drum and the opening through which the tube stub section projected.
Various tools have been suggested for removing these tubes by using wedges that are driven inside a bore of a structure, expanded for engaging the inside wall of a tube and retracted for pulling the tube out of the bore. For example, U.S. Pat. No. 4,355,450 to Miller discloses a tube extracting mechanism having a wedge with expandable circumferential gripping teeth.
Another method often used for removing tubing from structures is by use of a cutting torch. This is particularly common in the case of large boilers using heavy walled tubing on the order of three inches in diameter. Errors in use of the cutting torch can, of course, damage the tube sheet requiring expensive refinishing and repair work.
The primary problem with all these prior art structures is that they impose an expansion force on the tube precisely at the point where it is engaged with the tube sheet which can damage the metal between adjacent holes and cause the holes in the tube sheet to enlarge and not properly grip a new tube when it is expanded. Moreover, the prior art devices require additional moving parts which increase the likelihood of malfunctions and breakage of the device, which results in an increase of down-time of the structure for repairs.
Other tools for removing tubes include collapsing gripping devices for engaging the tube and pulling the tube out of the tube hole as exemplified in U.S. Pat. No. 6,205,632 to Weeks et al. and U.S. Pat. No. 4,180,903 to Hannigan, Jr. These prior art devices have complex and bulky structures comprised of a plurality of moving parts subject to easy breakage and expensive repair.
A simple device is needed without the complex and bulky structures of the prior art, requiring little or no repair.
Explosive force is known in the art for deforming metal. U.S. Pat. No. 3,228,757 to Verbraak which discloses a method for explosively deforming material, sheet, or metallic object having a mainly cubically face centered crystal lattice. Detonation of an explosive produces a shockwave directed at least substantially parallel to the direction of the crystal lattice.
Explosive force has been used to expand tubes or sleeves within a hole as taught by U.S. Pat. No. 4,879,890 to Hardwick and U.S. Pat. No. 5,983,487 to Snow et al. Explosives are also well known for welding tubes or sleeves, as exemplified in U.S. Pat. No. 5,022,148 to Feldstein et al., U.S. Pat. No. 5,038,994 to Feldstein et al., U.S. Pat. No. 4,641,774 to Krawchuk et al., and U.S. Pat. No. 3,377,010 to Suzuki et al.
As of yet, an explosive device has not been taught or suggested for removing tubes which have been expanded into fluid-tight pressure contact within a hole in a boiler, heat exchanger or the like.